As the integration density of semiconductor devices increases and the line width of circuits decreases, the demand for reducing the resistance of gate patterns has steadily increased. In order to reduce the resistance of gate patterns, metal layers having low resistance have often been used along with polysilicon layers. The sidewalls of a gate pattern including a metal layer may be abnormally oxidized during a thermal treatment, oxidation, or deposition process, and thus, the gate pattern may deteriorate.
In order to address this problem, research has been conducted on a method of preventing the oxidation of a metal layer by using preliminary spacers. These spacers cover the sidewalls of the metal layer and expose the sidewalls of a polysilicon layer during the oxidation of a gate pattern. Research has also been conducted on a method of selectively oxidizing a polysilicon layer using plasma containing a mixture of hydrogen and oxygen. However, the former method typically requires complicated processes and may cause the width of the gate pattern to decrease by as much as the width of the preliminary spacers due to a decrease in the design rule of a semiconductor device. Thus, the former method may result in an increase in the resistance of the gate pattern. Further, the latter method involves the use of a hydrogen plasma, and may thus cause damage to a gate substrate or a gate insulation layer and/or increase a leakage current.